The present invention relates generally to a packet relay system, and more particularly to a connecting function between communication networks to which the packet can not be reached directly because of their having packet routing protocols different from each other, and to an address translating function.
(Concept of Domain)
A domain has hitherto been defined as follows on a network layer.
[Domain]
The domain is a range where a packet can be forwarded based on a common routing control rule (protocol) on the network layer. Note that a packet reachability from one area to another area using different routing control rules (protocols) can not be attained unless through the relay system which can relay between the areas using different routing control rules (protocols).
The followings are examples of the domains different from each other.
Intra-organization Network (Intranet): Independent routing control based on Interior Gateway Protocol (IGP) is carried out in the Intranet, while in the Internet the routing control based in Exterior Gateway Protocol (EGP) is conducted. Generally, routing data in the Intranet are not distributed to the Internet.
IPv4 Network and IPv6 Network: These networks are capable of co-existence and neighboring as well through common communication media. The IPv4 network and the IPv6 network have, however, different network layer address systems, and therefore the routing data are not compatible with each other. Hence, The IPv4 network and the IPv6 network are managed by different routing control protocols.
IP Network and AppleTalk Network: These networks respectively use IP and AppleTalk (which is a protocol of Apple computer Corp., U.S.A) as protocols of the network layer. The address systems and routing data are not compatible. Hence, the IP network and the AppleTalk network are managed by the different routing control rules (protocols).
(Domains Based on Same Network Layer Protocol)
The respective networks operated based on the different network layer protocols are not compatible in terms of their routing data and therefore segmented into different domains.
On the other hand, a plurality of networks operated based on the same network layer protocol are compatible in terms of their routing data, and can be therefore integrated into one domain in principle. In fact, however, those networks might be intentionally segmented into a plurality of domains. The followings are examples of the reason why the plurality of networks operated based on the same network layer protocol are segmented into the plurality of domains.